(a) Field of the Invention
This invention relates to the technical field of structures and methods for mounting a resin panel to a car body member.
(b) Description of the Related Art
For the purpose of vehicle weight reduction, resin panels, instead of metal panels, have been frequently used in recent years as panels forming vehicles exteriors, such as fender panels. In such cases, the following problem may occur in painting process (a series of process steps including paint spraying, paint baking, paint film drying and cooling).
The painting process on panels, in some cases, is made to the whole car body with a plurality of panels mounted to car body members (normally made of metal) in order to prevent the plurality of panels from making a color difference. In these cases, if some or all of the panels are made of resin, a large difference in thermal expansion coefficient between the resin panel and the car body member (the former having a larger thermal expansion coefficient) causes that the resin panel expands more than the car body member at very high temperatures (for example, one hundred and several dozen degrees Celsius) of paint baking or paint film drying or contracts more when cooled later. As a result, the resin panel might be flexed and deformed.
For example, Unexamined Japanese Patent Application Bulletin No. 2001-206248 discloses a structure capable of absorbing a difference in thermal expansion coefficient between a resin panel and a metal car body member. This structure is a structure for fastening the resin panel and the metal car body member with bolts and nuts, in which the bolt insert holes in the metal car body member are formed of slots and the resin panel and the metal car body member are slidably fastened. With the use of this structure, when the resin panel expands or contracts more than the metal car body member owing to temperature changes, the resin panel moves relative to the metal car body member to allow expansion and contraction of the resin panel.
The structure described in the above bulletin, however, is inferred from the description to be for accommodating minute expansion and contraction in a natural environmental temperature range and to have no ability to accommodate large expansion due to high temperatures as during baking in painting process and contraction due to later cooling.
It can be considered as a method for accommodating large expansion and contraction in painting process that the bolts and nuts are preliminarily loosely fastened for accommodation of large expansion and contraction until the completion of the painting process and fastened to the end after the completion of the painting process. In this case, however, there is the possibility that in carrying or painting the resin panel as mounted to the car body member, the bolts and nuts might be dropped off owing to vibrations. Further, since the resin panel is painted with bolts and nuts preliminarily fastened, a paint film is formed on the surfaces of the bolts and nuts. Therefore, when the bolts and nuts are fastened to the end after the completion of painting process, the turning of the bolts and nuts may cause the paint film thereon to be peeled off, which might impair the appearance of the resin panel.